1. Field of the Disclosure
Embodiments disclosed herein relate generally to an actuation system for a downhole tool. In particular, embodiments disclosed herein relate to an actuation mechanism of a downhole tool to selectively open and close components of the tool.
2. Background Art
In the drilling of oil and gas wells, concentric casing strings may be installed and cemented in the borehole as drilling progresses to increasing depths. Each new casing string is supported within the previously installed casing string, thereby limiting the annular area available for the cementing operation. Further, as successively smaller diameter casing strings are suspended, the flow area for the production of oil and gas may be reduced. Therefore, to increase the annular space for the cementing operation, and to increase the production flow area, it may be desirable to enlarge the borehole below the terminal end of the previously cased borehole. By enlarging the borehole, a larger annular area is provided for subsequently installing and cementing a larger casing string than would have been possible otherwise. Accordingly, by enlarging the borehole below the previously cased borehole, the bottom of the formation may be reached with comparatively larger diameter casing, thereby providing more flow area for the production of oil and gas.
Various methods have been devised for passing a drilling assembly, either through a cased borehole or in conjunction with expandable casing to enlarging the borehole. One such method involves the use of an expandable underreamer, which has basically two operative states. A closed or collapsed state may be configured where the diameter of the tool is sufficiently small to allow the tool to pass through the existing cased borehole, while an open or partly expanded state may be configured where one or more arms with cutters on the ends thereof extend from the body of the tool. In the latter position, the underreamer enlarges the borehole diameter as the tool is rotated and lowered in the borehole. During underreaming operations, depending upon operational requirements of the drilling assembly, cutter blocks of the underreamer may be extended or retracted while the assembly is downhole.
Movement of the cutter blocks typically involves manipulating a sleeve that is used to open or close ports to allow fluid to activate and expand the cutter blocks of the underreamer. In certain prior art applications, the sleeve is held in place with shear pins, and a ball drop device may be used to shear the pins and thereby increase pressure in the tool to move the sleeve and open the cutter block activation ports. However, once the pins are sheared, the tool stays open for the duration of the drilling interval. Therefore, such a configuration may only allow one open cycle. This is also applicable in other tools which may be expanded, including but not limited to, cutting tools, spearing tools, and expandable stabilizers. Accordingly, there exists a need for an apparatus to allow the components of expandable tools to open and close multiple times while the tool is downhole.